Fathom crypt level 4? boss respawning

[DaSphinx]

After we took the goblin's bet for the quest on level 4 i think it was and killed this boss Xaxes or Xaxis ? we kept going on and I realized we forgot a room in the beginning so i went back and as i walked back through the area where we killed him he popped up with all his minions again on top of me.

So naturally i ran and we killed just the boss but the minions didn't need to die since the monster counter remained the same and we could move to the next level.

weird.

[Royce]

I think he respawns because he's needed for a quest and they do that sometimes so someone doesn't join the game and miss him. Respawning mobs never count toward the remaining counter.

[Snakespeare]

You can camp on him if you like, so long as you don't clear the map. He respawns about once every three minutes. I've done it, but have yet to get a good drop from him.